The present invention relates to an earphone without impulse noise for protection against conductive hearing loss, which can prevent the sound waves direction of loudspeaker thereof is not directly transmitted to the tympanic membrane located in the most inner side of external auditory canal. The middle ear can be protected against conductive hearing loss caused by the direct impact of the sound pressure.
It is conventionally know that the sound is defined as a physical energy and is transmitted in the form of energy. The farther the sound travels the greater energy it contains (like thunder or sound from gunshots). Therefore, energy in the sound is measured by the logarithm system while decibel(s) is often used as the unit to measure the sound intensity. However, the xe2x80x9cdecibelxe2x80x9d is not an absolute value, but a relative value, such that the decibel means a comparison of the intensity between two sounds. Hence, if we say how many decibels a sound has, it means that how many times its pressure greater than a certain reference one. When an audiometer is used to measure the hearing and the decibels increase from 0 to 60, it is indicated that the energy in the sound increases by 106. However, even a sound pressure with 60 decibels isn""t a loud sound, and it""s nearly equal to a great sound a few feet away from us in our daily life.
A human ear, as shown in FIGS. 1 to 3, consists of three main partsxe2x80x94the external ear 10, the middle ear 20, and the inner ear 30. The external ear 10 includes the helix 11, the antihelix 12, the auricle 13, the concha 14, the antitragus 15, the tragus 16, and the external auditory canal 17 whose length of an adult is about 24 mm. The tympanic membrane 171 is located in the most inner side of the external auditory canal 17. The external auditory canal 17 and the middle ear 20 are separated by the tympanic membrane 171 while the middle ear 20 is the ear drum formed between the external ear 10 and the inner ear 30 and having the malleus 21, the incus 22 and the stapes 23, wherein the end of the malleus 21 lies hidden in the tympanic membrane 171 while the body of the malleus 21 and the head of the incus 22 are joined together to be a joint. Besides, the incus 22 has a short leg 221 and a long leg 222, wherein the short leg 221 leans on the wall of the ear drum while the end of the long leg 222 is linked to the head of the stapes 23. The end of the stapes 23 is formed as a foot shape, as shown in FIG. 2.
Moreover, the inner ear 30 includes the cochlea 31 and the labyrinth 32, wherein the cochlea 31 controls the human hearing system while the labyrinth 32 maintains balance in the body. These two fine parts are enclosed by a capsule; in addition, some perilymphs in the most outer layer thereof cover the cochlea 31 and the labyrinth 32. These perilymphs are functioned as an air cushion to provide an excellent protection when the head gets an intense vibration. In fact, the cochlea 31 and the labyrinth 32 are floating in the fluid of the lymphs. The inside of the cochlea 31 consists of three partsxe2x80x94the scala vestibuli, the scala tympani, and the cochlear duct containing perilymph. The nerve cells in the cochlea 31 contain about 30,000 hairlike nerve endings. Besides, the oval window 33 and the round window 34 are located near the wall surface of eardrum of the middle ear 20 while the base of the stapes rests against the opening of oval window 33 and the inner side thereof is attached to the scala vestibuli 311 of the cochlea 31 so that the cochlea 31 can receive the sound pressure transmitted from the auditory ossicies while the round window 34 is attached to the scala tympani 312 of the cochlea 31 in order to directly receive the sound transmitted from the eardrum of the middle ear 20.
Furthermore, after the sound pressure is transmitted from the tragus 17 to the tympanic membrane 171, a portion of the sound pressure is partially reflected back to the tragus 76 while another portion of the sound pressure passes through the tympanic membrane 171 into the middle ear 20. The portion of the sound pressure that has been transmitted into the middle ear 20 has a certain part pass through the malleus 21 and the incus 22 into the foot-shaped end of the stapes 23 (those who consist of the malleus 21, the incus 22, and the stapes 23 is hereafter called auditory ossicles), and then through the oval window 33 into the cochlea 31 of the inner ear 30. The rest of the sound pressure is transmitted by the air medium in the eardrum into the cochlea 31 of the inner ear 30.
Consequently, the sound pressure transmitted into the human ear is divided into two parts to enter the inner ear 30; however, the sound transmitted by the way of auditory ossicles into the oval window 33 is more effective and important than that transmitted by the air medium through eardrum into the round window 34. The reason is that 99.9% of the energy of the sound pressure transmitted into the eardrum of the middle ear 20 and passing by way of the air medium through the round window 34 into the perilymph of the cochlea 31 is consumed or reflected back by the fluid surface. Only 0.1% of the energy is able to pass through the perilymph into the cochlea 31.
Accordingly, the most effective way of the sound transmission is carried out from the tympanic membrane 171 through the auditory ossicles into the oval window 33. However, when the sound pressure is transmitted to the end of the stapes 23 and strikes the oval window 33, it directly passes through the incompressible perilymph into the cochlea 31 while the sound pressure is not consumed or reflected by the fluid surface. Presently, the perilymph containing the sound pressure stimulates the hairlike nerve endings in the cochlea 31 to generate a displacement or a bending, and this motion can turn the mechanical force in the sound pressure into electrochemical impulses that are carried up the acoustic nerve to auditory cortex of the brain. At last, it is the sound we can understand.
In view of the above, we realize that sense of hearing of the human ear is generated by the movement of the hairlike nerve endings, that even a slight displacement of the hairlike nerve endings causes the sense of hearing. Therefore, the sense of the human ear is very sharp and the perceptible pitch is also very wide. Generally, the perceptible frequency range of human beings is about 20xcx9c20000 Hz while the intensity range 1012xcx9c102 W/m2 and the sound pressure less than 180 dB. However, not all perceptible sounds are suitable for the human ear to receive. The pitch in the improper range (sound pressure over 90 dB is so-called noise) easily causes the damage of the auditory part in the ear. The factory workers under a long-time exposure to the industrial noise without wearing any hearing protectors (like earplug or earphone) have the hearing damage possibility up to 25% after a few years.
The reason lies in that the sound pressure of the industrial noise stimulates the hairlike nerve endings in the ear to generate a displacement or a bending. They return to the original state when leaving this noise circumstance for a period. The restoring effect of the hairlike nerve endings worsens more and more with the time and causes the hearing damage in the inner ear. This kind of hearing loss mostly belongs to the perceptive hearing threshold while the other kind is mostly caused by a direct strike on the head or an instant impulse noise, resulting in a damage of the ear membrane or the auditory ossicles so that the sound pressure transmitted in the middle ear 20 simultaneously enters the oval window 33 and the round window 34 in the vestibuli 33 and it is counteracted by each other. Accordingly, a hearing loss is caused. This kind of conductive function loss in the middle ear is called conductive hearing loss.
Obviously, the hearing loss resulting from the above mentioned kind of conductive function loss in the middle ear increases in these years, and most of them are the young people using Walkman. It is well-known that the loudspeaker of the common stereophonic sound or the earphone is driven by the current connected by the electric cord so that the conic paper box on the front part and the vibrating membrane generate a to and fro vibration to produce sound and music. A complicate physical phenomenon is produced by this simple, to and fro repetitive movement that the air is compressed when the conic paper box on the front part and the vibrating membrane move forward so that the molecules in the air become dense to be the high pressure air while the molecules in the air are thinned to be the low pressure air when the conic paper box on the front part and the vibrating membrane move backward.
However, the air molecules have the same characteristics as we don""t like to be compressed and squeezed, so that an elasticity is generated by the squeezed air to push the energy produced by the loudspeaker to a farther place. When the loudspeaker proceeds with the to and fro movement, the adjacent air pushes the energy forward by this loudspeaker. This energy pushing the sound transmission is called xe2x80x9csound pressurexe2x80x9d.
Accordingly, the sound energy transmission is a continual connection between a high pressure space and a low pressure space. This pressure space as the wave includes the wave peak and the wave valley which move forward unceasingly, so that the moving direction of the sound produced by the loudspeaker is completely driven by the sound pressure and the people in the farther place is also able to hear the sound or music produced by the loudspeaker.
Furthermore, the transmission way and the distribution state of the sound produced by the loudspeaker depend on the frequency of the loudspeaker. For example, the low tone of sound itself has no direction. When it sounds, it is slowly propagated to all directions. Therefore, the furnishing place for the super low tone is not so demanding as the common loudspeaker while the propagation way of the high tone of sound is similar to laser rays whose proceeding direction is almost straight, so that surfaces resulting in reflection should be prevented for the furnishing direction of the high tone body from the counteraction of tone quality and the destruction of the sound field. In other words, the sound pressure is the same in all of the propagation directions when the loudspeaker sounds. However, the front direction of the loudspeaker must face the continual double impact of the sound pressure and the high tone. Thus, a strong feeling and an obvious vibration are produced when we are hearing the Rock and Roll of the heavy metal music or fast rhythm music.
The loudspeaker makes use of the vibration to propagate the converted sound or music signal to a space to form a sound field. So, we have a strong vibration feeling when we get a strong sound pressure in a sound field; we don""t have a strong feeling when we are in a slight sound pressure. However, we are still within the vibration range of the sound field. So, we receive impact vibrations of the sound pressure when we are in the sound field, no matter which music or sound is played, even the small loudspeaker installed in the earphone has its own sound field range. The difference only lies in the different intensity.
The conventional earphone has two types. One is the earplug type and the other is earmuff type. Whichever earphone is used, its loudspeaker is placed near the outer opening of the external auditory canal while the right side of the loudspeaker is opposite to the tympanic membrane inside the external auditory canal of the ear so as to enable the ear to directly receive sound or music from the loudspeaker. Though an excellent tone quality is able to be received by the ear through this way due to the fact that the ear is within the sound field range of the loudspeaker and the sound pressure is vibrating between the loudspeaker and ear membrane. Moreover, the sound pressure from the earphone is about 10 dB higher than that from the common loudspeaker with respect to the same sound received by the ear. In addition, the sound pressure generated by the earphone of the Walkman is always over 90 dB; therefore the conductive function loss of the middle ear or the hearing loss is easily caused by such strong sound pressure and the unceasing impact noise.
The applicant is a licensed doctor having clinic experiences for years. Since patients with hearing loss seeking medical counsel are more and more young people and the applicant found that the reason for that lies in the use of the Walkman resulting in the damage of conductive function in the middle ear. Besides, the impulse noise is the main reason for the damage of the tympanic membrane and the auditory ossicles.
Accordingly, it is a main object of the present invention to provide an earphone by which the splendid music is able to be heard as by the conventional earphone and the conductive function of middle ear is protected against damage resulting from impulse noise.
It is another object of the present invention to provide an earphone without impulse noise for protection against conductive hearing loss, in which both the sound emitted by the loudspeaker in the earphone and the sound outsides can be caught by the ear, so that any events outside can be realized at once without taking off the earphone.